ACTIN AND MAJOR SPERM PROTEIN IN SPERMATIDS AND SPERMATOZOA OF THE PARASITIC NEMATODE HELIGMOSOMOIDES-POLYGYRUS

Nematode spermatozoa are amoeboid cells. In Caenorhabditis elegans and Ascaris suum, previous studies have reported that sperm motility does not involve actin, but, instead, requires a specific cytoskeletal pro tein, namely major-sperm-protein (MSP). In Heligmosomoides polygyrus, a species with large and elongate spermatids and spermatozoa, cell org anelles are easily identified even with light microscopy. Electrophore sis of Heligmosomoides sperm proteins indicates that the main protein band has a molecular weight of about 15 kDa, as MSP in other nematodes , and is specifically labelled by an anti-MSP antibody raised against C. elegans MSP. A minor band at 43 kDa was specifically labelled by an anti-actin antibody. Reaction of anti-actin and anti-MSP antibodies i s specific to, and restricted to, their respective targets. Actin and MSP localisation, studied by indirect immunofluorescence in male germ cells of Heligmosomoides polygyrus, are similar: spermatids show rows of dots, corresponding to the fibrous bodies, around an unlabelled cen tral longitudinal core; spermatozoa are labelled strictly in an anteri or crescent-shaped cap, at the opposite pole to the nucleus, which con tains fibres of the MSP cytoskeleton. Phalloidin labelling shows that F-actin is present in spermatids, but absent in spermatozoa. Tropomyos in shows a distinct pattern in spermatids, but is located in the MSP a nd actin-containing cap in spermatozoa. It is hypothesized that actin plays a role in the shaping of the cell and in the arrangement of its organelles during nematode spermiogenesis, when MSP is present, in an inactive state, in the fibrous bodies. The concentration of actin and tropomyosin in the anterior cap is not compatible with previous theori es about the MSP cytoskeleton, which is supposed to act in the absence of actin. (C) 1996 Wiley-Liss, Inc.